The present invention relates to pulse welding equipment for welding by using a welding wire and outputting pulse peak current and base current alternately, and a method of controlling the same.
A control method of pulse welding equipment of a prior art disclosed in Japanese Laid-open Patent No. 4-270069 is described below while referring to FIG. 4A and FIG. 4B. FIG. 4A shows the lapse of time relating to the position of the welding wire tip end upon arc starting and the arcing. When forming an arc 4 between a welding wire 2 supplied to a nozzle 1 at the tip end of a welding torch and a base metal 3, it shows the process consists of the following subsequent steps:
(a) a state before start of welding,
(b) a short-circuited state of welding wire 2 and base metal 3 just before arc starting,
(c) a flare-up state of welding wire 2,
(d) a transitional state until reaching a stable state of appropriate arc length for main welding, and
(e) the stable state of appropriate arc length for main welding.
On the other hand, FIG. 4B schematically shows the lapse of time of the welding current corresponding to FIG. 4A, that is:
the state (b) just before arc starting is immediately followed by a hot current output period (TH period),
an initial current output period for flaring up the welding wire 2 continues (TINI period), being followed by
a transition period to main welding current by changing from high frequency to low frequency in gradual steps (TSLP period), and
a main welding current output period (TW period).
The welding currents outputted in each period of TH, TINI, TSLP, and TW are represented by IH, IINI, ISLP, and IW respectively.
In such conventional control method of pulse welding equipment, in the process of transition of arc length from state (c) to state (e), the pulse welding frequency is changed in gradual steps from high frequency to the frequency of main welding state, and in the TSLP period (d), the arc length is gradually shortened. It helps to lower the incidence of short-circuiting between the welding wire and base metal in the course of transition from right after arc starting until the arc length of main welding condition, and decrease the generation of spatter by short-circuiting.
However, in the conventional control method of pulse welding equipment, because of the provision of TSLP period for changing from high frequency to low frequency in gradual steps, it took a long time until the arc was stabilized at a proper length for main welding. By this method, generation of spatter by short-circuiting is decreased. But, to the contrary, spatter was generated due to abnormal growth of droplets at the tip end of the welding wire 2. Further, as the welding wire 2 flares up, the state of long arc length continues for a while, and the area of the arc 4 contacting with the base metal 3 is wider. Therefor the deposition quantity of the wire 2 on the base metal 3 in unit area decreases, and the heat affected zone of the base metal 3 is widened.
It is hence an object of the invention to present pulse welding equipment for starting an arc smoothly, and its control method.
To achieve the object, the pulse welding equipment of the invention comprises:
(a) means for feeding a welding wire,
(b) means for feeding a pulse current between the welding wire and base metal, and
(c) means for controlling this pulse current feeding means;
in which the control means controls the pulse current feeding means so as to flare up the welding wire upon arc starting, and controls the pulse current feeding means until the pulse current becomes lower in frequency than the pulse frequency of the main welding current.
From flare-up of welding wire following arcing when starting welding until output of main welding current, it is designed to output a pulse current of lower frequency than the pulse frequency of main welding current.